Hays' "Echoes of Scripture in the Letters of Paul"
The first big point Hays makes is the overall theme of the book -- that the Old Testament Scriptures formed the woof and weave of the sources upon which Paul drew. I guess this is a controversial proposition in some circles. Nonetheless, pick up commentaries or sermons from ancient times to modern, and we see authors turning to the Old Testament to understand Paul use of those Scriptures.
The second big argument Hays advances is that Paul's letters are "ecclesiocentric" rather than "Christocentric."
I think there's an important insight in that claim. But Hays takes it too far. He seems to want to run a dividing wall between the two concepts, essentially claiming that what is predicated of Christ cannot also be predicated of the church, and vice versa. So, he concludes, Paul just basically disagrees with the more Christocentric New-Testament authors.
I don't buy it. If one takes the idea that the church is the body of Christ as a central concept in Paul's letters -- and I do -- then ecclesiocentricity and Christocentricity cannot be pitted against one another. Paul's letters are "ecclesiocentric" because of the distinctive nature of his ministry expressed through these letters to these churches. But this hardly makes these letters any less Christocentric in principle. What is predicated of Christ can be predicated of his body, the church. (That's probably an overstatement, but it's true enough with regard to the elements of Hays' argument.)